285 lines
12 KiB
ReStructuredText
285 lines
12 KiB
ReStructuredText
.. _concepts_magnitudes:
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Amplitudes and Magnitudes
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#########################
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:ref:`Magnitudes of specific types <concepts_magnitudes-station>` are computed
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from :ref:`amplitudes <concepts_magnitudes-amplitudes>` measured on waveforms.
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Different types of amplitudes and magnitudes are available including aliases.
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All magnitudes can be regionalized and mapped to Mw. The native amplitude and
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magnitudes types are listed in :ref:`scamp` and :ref:`scmag`.
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All amplitude and magnitude values can be read in the Magnitudes tab of
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:ref:`scolv`, in bulletins created by :ref:`scbulletin` and dumped
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from database to XML for an origin or event by :ref:`scxmldump`.
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This concept section describes the principles applied in |scname| and links to
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more specific sections including tutorials describing the configuration and
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application.
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.. figure:: media/amplitude-magnitude-processing.png
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:alt: amplitudes and magnitudes: processing flow
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:align: center
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:width: 18cm
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Schematic processing flow for computing magnitudes from measured amplitudes
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including the involved |scname| modules and interfaces. Multiple network
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magnitude types can be computed for the same :term:`origin`. The default
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processing of native amplitudes and magnitudes in the center can be extended
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by aliases, regionalization, Mw mapping or external magnitudes.
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.. _concepts_magnitudes-amplitudes:
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Amplitudes
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==========
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Amplitudes can be measured on waveforms
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* Automatically during phase picking by :ref:`scautopick` with generally fixed
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time windows due to the absence of knowledge about source parameters.
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* Automatically by :ref:`scamp` as soon as :term:`origins <origin>` are
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available. Depending on the amplitude type and their configuration, fixed or
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distance-dependent time windows as well as constraints on signal quality apply.
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* Interactively using :ref:`scolv` with preset or user-defined conditions.
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:ref:`Time grammar <time-grammar>` applies for configuring the time windows.
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Input data
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----------
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Depending on type amplitudes are measured on raw or filtered waveform data.
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Initial raw data are given in counts of the digitizer with a stream gain unit of
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m/s which is typical for seismometers.
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It is assumed that the measured signal has its dominant
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frequency where the response of the recording instrument is flat.
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For other instruments such as accelerometers or short-period geophones, amplitude
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correction for instrument response and the corresponding frequency range may be
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configured by the global binding parameters
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:confval:`amplitudes.enableResponses`, :confval:`amplitudes.resp.minFreq`,
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:confval:`amplitudes.resp.maxFreq` or even with in amplitude-type profiles for
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more specific application. Amplitude measurements will fail if the
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unit of the (corrected) input data do not correspond to the requirement of the
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amplitude type.
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Filtering may involve
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:ref:`simulation of Wood-Anderson seismographs <concepts_magnitudes-wa>`.
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Final amplitude measurements are corrected by stream gain and provided as an
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amplitude object.
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.. _concepts_magnitudes-wa:
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Wood-Anderson simulation
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------------------------
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Some amplitude types require or allow the correction of waveforms by simulation
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of instruments such as :py:func:`Wood-Anderson torsion seismometers <WA>`
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(:cite:t:`richter-1935,uhrhammer-1990`), :py:func:`WWSSN_SP` or :py:func:`WWSSN_LP`.
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The calibration parameters describing a Wood-Anderson seismometer are
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configurable in global bindings or module configuration:
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:confval:`amplitudes.WoodAnderson.gain`, :confval:`amplitudes.WoodAnderson.T0`,
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:confval:`amplitudes.WoodAnderson.h`. Specifically, the difference in magnitude
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due to configuration using original values listed in
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:cite:t:`richter-1935` and updated ones given in :cite:t:`uhrhammer-1990`
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result in a constant offset of 0.13 in those magnitudes which apply
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Wood-Anderson simulation, e.g. :term:`ML <magnitude, local (ML)>`,
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:term:`MLv <magnitude, local vertical (MLv)>`, :term:`MLc <magnitude, local custom (MLc)>`.
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Physical units
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--------------
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The physical units of measured amplitudes depend on amplitudes type. They are
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documented along with the corresponding magnitude type. Starting with the initial
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gain unit of raw data streams, typically m/s, the amplitude processor in
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|scname| converts to the required unit. Where instrument simulation if optional,
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e.g., for :term:`MLc amplitudes <magnitude, local custom (MLc)>`, a conversion
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configurable factor must be considered for non-default amplitude processing.
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.. _concepts_amplitudes-aliases:
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Amplitude Aliases
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-------------------------------
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New amplitude types (aliases) can be created based on existing amplitude types
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but configured and measured specifically. They can be measured as any other
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amplitude by :ref:`scamp` or :ref:`scautopick` and used by other modules, e.g.,
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by :ref:`scmag` for :ref:`magnitude aliases <concepts_magnitudes-station>`. The
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setup procedure is outlined in the tutorial on
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:ref:`amplitude aliases <tutorials_amplitude-aliases>`.
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.. _concepts-amplitudes-regionalization:
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Regionalization
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---------------
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Measuring amplitudes only for sources or pairs of sources and stations in
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specific regions is supported by regionalization. The region polygons are
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defined by :ref:`magnitude regionalization <concepts-magnitudes-regionalization>`.
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In order to use the feature, regionalized amplitudes and magnitudes must have
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the same type (name) and regionalization must be activated per amplitude type in
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amplitude-type profiles of global bindings.
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.. _concepts_magnitudes-station:
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Station Magnitudes
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==================
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Station magnitudes are computed automatically by :ref:`scmag` or interactively
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by :ref:`scolv` from measured amplitudes based on distance-dependent
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calibration curves which depend on magnitude type. Since distance measures are
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required, station magnitudes are always related to one :term:`origin`. For
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computing new magnitudes in scolv, a new origin must be created which is done by
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relocating.
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When computing a set of station magnitudes in :ref:`scolv` which is different from
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the set configured in :ref:`scmag`, then scmag may later add the missing
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magnitudes automatically. Magnitude types for which the evaluation status is
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set to "rejected", e.g., in :ref:`scolv`, will not be recomputed by scmag. In
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order to ignore a magnitude type interactively, it should therefore be treated
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and rejected in scolv.
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.. _concepts-magnitudes-correction:
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Station corrections
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-------------------
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Linear station corrections applied to station magnitudes can be configured by
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global :ref:`binding parameters <global_bindings_config>`:
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#. Add a magnitude type profile where the name of the profile is the name of the
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magnitude itself,
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#. Configure the correction parameters.
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When using binding profiles, all referencing stations will be affected equally
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which is typically not intended. In contrast, applying station bindings requires
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to set up many bindings which may not be intended either.concepts-magnitudes-regionalization
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Therefore, you may add lines to the global module configuration in
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:file:`global.cfg` where one line corresponds to one station with one magnitude
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and the corresponding correction parameter. The groups and the name of the
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parameters are identical to the global bindings parameters. All lines start with
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"*module.trunk*". Example for an offset correction of
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:term:`MLv <magnitude, local vertical (MLv)>` measured station GE.UGM:
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.. code-block:: properties
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module.trunk.GE.UGM.magnitudes.MLv.offset = 0.1
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.. note::
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The configuration of parameters starting with *module.trunk.* is not
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supported by :ref:`scconfig`. All corresponding configurations must be done
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by direclty editing the configuration file, e.g.,
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:file:`seiscomp/etc/global.cfg`.
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.. _concepts_magnitudes-aliases:
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Magnitude Aliases
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-------------------------------
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New magnitude types (aliases) can be created inheriting the configuration
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parameters but not the configured values from existing magnitude and amplitude types or
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:ref:`amplitude aliases <concepts_amplitudes-aliases>`. The values are configured
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specifically. Unless specified explicitly, the amplitude type
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is the base amplitude of the original magnitude. Other
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amplitude types or amplitude aliases must be defined first and given explicitly.
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The aliased magnitudes can be computed by other modules such as :ref:`scmag` or
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:ref:`scolv`. The setup procedure is outlined in the tutorial on
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:ref:`magnitude aliases <tutorials_magnitude-aliases>`.
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.. _concepts-magnitudes-regionalization:
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Regionalization
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---------------
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The computation of station magnitudes can be regionalized. This means that for
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a specific region specific conditions apply when computing magnitudes. The
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conditions include any parameter available for configuring a magnitude
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including global binding parameters such as magnitude calibration, distance
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and depth ranges, etc. As an example you may wish to apply different
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attenuation curves for computing MLv magnitudes to earthquakes in Eastern and
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in Western Canada.
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Regionalization is achieved by adding magnitude-type profiles in the magnitudes
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section of global module configuration parameters. Regionalization assumes
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defaults from global bindings but overrides the values when configured. The
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setup procedure including
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:ref:`station corrections <concepts-magnitudes-correction>` is outlined in the
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:ref:`tutorial on regionalization <tutorials_magnitude-region-aliases>`.
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.. _concepts_magnitudes-network:
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Network Magnitudes
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==================
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Network magnitudes are computed automatically by :ref:`scmag` or interactively
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by :ref:`scolv` from station magnitudes based on averaging station magnitudes.
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The averaging methods applied by :ref:`scmag` are configurable by
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:confval:`magnitudes.average`. Available are (:cite:t:`rosenberger-1983`):
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* *mean*: The mean value from all station magnitudes.
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* *median*: The mean value from all station magnitudes.
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* *trimmedMean(X)*: Ignores outlier station magnitudes by first removing the
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largest and the smallest *X* % of the observed values (percentiles). The mean is
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formed from the remaining station magnitudes.
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* *trimmedMedian(X)*: Forms the median from all station magnitudes but returns
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the uncertainty by ignoring the largest and the smallest *X* % station
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magnitudes.
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* *medianTrimmedMean(X)*: Returns the mean magnitude from all station magnitudes
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differing less than *X* magnitudes from the median.
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.. _concepts_magnitudes-moment:
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Moment Magnitudes
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=================
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Moment magnitudes can be derived from all other network magnitudes by mapping of
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the original network magnitude, e.g., *Mx*, to a new moment magnitude *Mw(Mx)*.
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The mapping function can be configured for all original magnitude types except
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:term:`mB <magnitude, derived mB (Mw(mB))>` and
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:term:`Mwp <magnitude, derived Mwp (Mw(Mwp))>` where the mapping is hardcoded.
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Read the :ref:`tutorial on moment magnitudes <tutorials_mags_moment>` for the
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configuration.
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.. _concepts-magnitudes-summary:
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Summary Magnitude
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=================
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In order to account for different phenomena related to magnitude computation
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including magnitude saturation and application of different magnitude types at
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specific distance and depth ranges of the sources a summary magnitude can be
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computed from network magnitudes by :ref:`scmag`. The summary magnitude is
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usually referred to as *M*. The name is configurable.
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.. note::
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Station, network and summary magnitudes are contained uniquely in one
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:term:`origin`.
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.. _concepts_magnitudes-preferred:
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Preferred Magnitude
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===================
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From the list of computed network magnitudes and the summary magnitude,
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:ref:`scevent` can automatically determine the preferred magnitude of the
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:term:`event`. This may also be done interactively by operators in the
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:ref:`Event tab of scolv <scolv-sec-event-tab>` or by
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:ref:`custom commit buttons in scolv <sec-scolv-custom-commit>`.
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